Related Experiment Videos
Synthesis and processing of the major envelope glycoprotein of murine cytomegalovirus
1Department of Microbiology, University of Saskatchewan, Saskatoon, Canada.
Abstract:
We have characterized the synthesis and processing pathway of the major envelope glycoprotein complex of murine cytomegalovirus (gp52/105/150). We have demonstrated that it belongs to the "late" kinetic class of MCMV proteins, and is initially synthesized as a 128K glycoprotein (gp128) which contains N-linked, high-mannose type oligosaccharide chains and is phosphorylated predominantly at serine residues. A fraction of the gp128 molecules also contains O-linked GalNAc residues. The majority of the gp128 molecules appears to be retained in the endoplasmic reticulum as evidenced by their sensitivity to endoglycosidase H digestion. The formation of disulfide linkages and dimerization allow the transport of gp128 to the Golgi compartments where modification of N-linked carbohydrate structures and extension of O-linked oligosaccharide chains take place, cumulating in the appearance of the mature gp150. The final processing step involves the cleavage of gp150 into gp52 and gp105. By blocking the transport of the glycoprotein precursor to the trans-Golgi compartments with the ionophore monensin, the cleavage process is inhibited, suggesting that the trans-Golgi compartment is the site where gp150 is cleaved. However, the cleavage process is incomplete, resulting in the formation of multiple disulfide-linked complexes made up of different combinations of gp52, gp105, and gp150. Therefore, the processing of the major envelope glycoprotein complexes of murine cytomegalovirus resembles that of the gcl/gp55-116 complex of human cytomegalovirus.
Insights
Murine cytomegalovirus (MCMV) envelope glycoproteins are synthesized as gp128, processed through the endoplasmic reticulum and Golgi, and cleaved into gp52/105. This pathway resembles human cytomegalovirus glycoprotein processing.
Area of Science:
- Virology
- Molecular Biology
- Glycoprotein Synthesis and Processing
Background:
- Murine cytomegalovirus (MCMV) is a significant pathogen, and understanding its envelope glycoproteins is crucial for antiviral strategies.
- The major envelope glycoprotein complex of MCMV plays a vital role in viral entry and pathogenesis.
Purpose of the Study:
- To characterize the synthesis and processing pathway of the major MCMV envelope glycoprotein complex (gp52/105/150).
- To elucidate the specific cellular compartments and molecular events involved in glycoprotein maturation.
Main Methods:
- Analysis of glycoprotein synthesis kinetics, identifying MCMV proteins belonging to the 'late' kinetic class.
- Biochemical characterization of the precursor glycoprotein (gp128), including N-linked and O-linked oligosaccharide modifications and phosphorylation.
- Endoplasmic reticulum (ER) and Golgi localization studies using endoglycosidase H digestion and ionophore monensin treatment to block transport.
Main Results:
- MCMV major envelope glycoprotein complex is initially synthesized as a 128K glycoprotein (gp128) with high-mannose N-linked glycans and serine phosphorylation.
- gp128 undergoes disulfide bond formation and dimerization in the ER, followed by N- and O-linked glycan modifications in the Golgi, forming gp150.
- gp150 is cleaved into gp52 and gp105 in the trans-Golgi, though incompletely, yielding heterogeneous disulfide-linked complexes.
Conclusions:
- The processing pathway of the MCMV major envelope glycoprotein complex involves sequential modifications and cleavage within the ER and Golgi.
- The trans-Golgi network is identified as the primary site for gp150 cleavage into gp52 and gp105.
- The processing mechanism shares similarities with the glycoprotein processing of human cytomegalovirus (HCMV).